What's a Limewire Document?

I'm just getting started with Limewire. The first 2 files I downloaded worked fine. They showed up in my Shared Folder as Quicktime files which played fine with iTunes. Everything I've downloaded since has appeared in my Shared Folder as a Limewire Document. It doesn't play, and it can't be converted to an mp3. Why is this happening? Is this normal?

Any help would be appreciated.